OK, what airplane ARE you flying? "Not so aerobatic" does not help. Is it a glider, Warbird, trainer, quickie 500, extra, cub.... what is it?

Snap Roll by AMA aerobatics code is "a simultaneous, rapid autorotation in the pitch, yaw and roll axes in a stalled wing attitude."

Now, to do a snap roll there are some things the plane must do.
1. You need to increase the angle of attack to put the plane into a position where it will stall. This is done with a quick pulse of up elevator to "break" the nose and put the wing in a position to stall.
2. Within a split second of that pulse of elevator input you push the rudder full over (to start learning to snap) and at the same time input full aileron deflection in the same direction as the rudder.
**What you should see then is called "rapid autorotation". When you input the rudder you get "YAW" which means one wing speeds up, and the other slow rapidly and stalls. This initiates a sharp roll in the direction of the rudder input becuase one wing stops flying. Technically you should not "Need" to use ailerons, but with RC models the ailerons help to get the process started. You should not be depending on the ailerons for the rotation, if you are its not snapping they are just there to clean it up a little.
3. To keep the plane on heading as stated about you neutralize the elevator 1st and then the ailerons and rudder. All of this happens in less than 1 second.

Again,
Initiate stall in the wing by sharply pitching.
Stall the wing by inputting the rudder
Ailerons to clean up the rotation.
Neutralize at just the right moment to stop roll.

It is sortof a J pattern laid on its side.